Is cancer due mostly to “bad luck”?

One of the more difficult conversations to have with a patient as a cancer doctor occurs when a patient, recently informed of her diagnosis of, for example, breast cancer, asks me, “Why did I get this? What caused it?” What almost inevitably follows is an uncomfortable conversation in which explanations of the multiple known causes of breast cancer do not satisfy the patient. The reason, of course, is because when a patient asks, “What caused it?” she doesn’t mean what causes breast cancer in general or in statistical terms. Rather, she means, what caused my breast cancer? It’s a question that can only occasionally be answered. For instance, if it’s lung cancer and the patient is a smoker, then it was almost certainly smoking that caused the cancer, because lung cancer is a relatively rare cancer in the absence of smoking. In the case of breast cancer, contrary to the prevailing belief that leads women with breast cancer to be puzzled about how they could get it when there’s “no cancer” in their families, only around 5-10% of cases have a familial or genetic component. That means that around 90% of breast cancers are what we call “sporadic,” which means that we can’t identify a specific cause. Or, as I like to say, “We just don’t know.” Worse, in the case of breast cancer, the environmental factors we know about appear to contribute modestly at best to the risk of cancer. (More on this later.)

Understandably, patients hate hearing “We just don’t know,” some vague handwaving about genes, and that there is nothing that we know of that they did that caused their cancer. People—including oncologists—really don’t like the concept of “sporadic” cancer, mainly because humans crave explanation. The default assumption is that everything must happen for a reason and there must be a cause for every disease or cancer. Perhaps the most ridiculously emphatic statement of this that I’ve encountered thus farcomes from (who else?) über-quack Mike Adams when he heaped contempt on the idea of sporadic disease as “spontaneous disease.” He did this in the context of a story describing how, after Dr. Mehmet Oz had followed recommended care and undergone screening colonoscopy to look for polyps, he was shocked that he actually had some. This led Adams, in his usual inimitable fashion, to construct a straw man so massive that it could be seen from space when he set it on fire, declaring that “colon polyps, in other words, appear without any cause!” and that “mainstream medicine…believes in the theory of ‘spontaneous disease’ that ‘strikes’ people at random.”

Not exactly.

On the other hand, there is a lot of randomness in disease, not just cancer, as hard as it is for Mike Adams, or anyone to accept. Just because there is a varying amount of randomness in who gets a disease does not mean that mainstream medicine claims there is no cause to these diseases. Rather, for diseases like cancer, it’s a stochastic process, meaning that chance can play a role—sometimes a big role—in determining who gets sick. Indeed, just last week there was more evidence supporting this idea published in Science. Unfortunately, much of the mainstream press coverage presented the message of the paper a bit too simplistically. Even more unfortunately, it was the authors who encouraged this, as did the Johns Hopkins University press release about the study, which was entitled “Bad Luck of Random Mutations Plays Predominant Role in Cancer, Study Shows“. Yes, I groaned when I read this title.